Furnace for the production of aluminum



July 1, 1930. E. R. LAUBER FURNACE FOR THE PRODUCTION OF ALUMINUM 1mm June '28, 1926 l MOLTE/V aLuM/N/u/v 6PM PH/TE MGLTE/V ALVM/AIIUM Patented July 1.1930

UNITED TATES v ERWIN RICHARD LAUIBER, OF EMMISHOFEN, SWITZERLAND FURNACE FOR THE PRODUCTION OF ALUMINUM Application filed June 28, 1926, Serial No. 119,159, and in Germany July 80, 1925.

For the electrolytic separation of aluminum furnaces have hitherto chiefly been employed in which the supply of current to the actual liquid aluminum cathode is effected 6 through an auxiliary cathode which serves at the same time as the furnace bottom. This auxiliary cathode consists of iron or copper covered with a compressed carbon mass,

which on the one hand forms the medium of 10 current supply between the iron or copper auxiliary cathode and the liquid cathode,-and

on the other handprotects this metallic auxiliary ,cathode from attack by the liquid aluminum. Such furnace bottoms have, in

' new furnaces, a transition resistance in favourablecases of- 0.4 volt which gradually rises to from Ito 1.5 volts. The actual aluminum cathode is consequently heatedaccor ding to the resistance-of the furnace bottom,

9 which is very undesirable, but up to the present has'been found unavoidable.

Of the electrical energy introduced into the aluminum furnace about .per cent on an average is used for the production of alu- 5 minum, while the rest is radiated in the form of heat. {Part of the electrical energy radiated in the form of heat could be saved, if the furnace,,and more particularly the furnace bottom, could be thermall insulated to pre- 30 vent losses of heat. In t e case of the furnace bottoms hitherto employed such thermal insulation is impossible. The thermally insulated carbon bottom could only give up to the aluminum cathode the heat produced in consequence of its resistance, which, in consequence of the overheating'of the aluminum, would lead to poor'current utilization and would quickly destroy the furnace bottom. On this account the metallic auxiliary cath- 40 ode, and with it the carbon. bottom, have hitherto been suitably cooled by means of air.

According to the present invention the current is supplied to the liquid aluminum cathode by means of-graphite blocks in any suitable and convenientmanner. It is "sufli'cient to suspend one or more blocks of graphite in the liquid bath from above until they touch the liquid aluminum cathode. The graphite block or blocks take over the conducting of "ply the current to the aluminum cathode are by liquid aluminum. Blocks. or rammed the current. and do it in such an advantageous manner that the resistance of the graphite current supply, including the resistance of the liquid aluminum cathode, moves constantly in the order of magnitude of 0.1 volt. The graphitic current supply to the liquid aluminum cathode may also be effected in any convenient and suitable manner by embedding the graphite blocks in the sides or bottom of the furnace, provided care is taken that the 'graphitic surface always remains in direct contact with the aluminum cathode.

Certain ways in which it is possible to supillustrated in the accompanying. drawings. In these drawings the letter a indicates the thermal insulation, 6 the furnace bottom made of mineral substances, 0 the graphite mass, (5 and d the current supply, 2 the liquid molten aluminum f the molten cryolite, g the electrodes forming the anode and k a compressed carbon mass.

Since, in graphitic current supply, which has practically no resistance, even when supplying the current from the bottom of the furnace, no heating action takes place, the metallic auxiliary cathode and also the layer of compressed carbon hitherto utilized between the metallic auxiliary cathode and the liquid metal, are both superfluous.

According to the present invention therefore the bottom of the furnace may be made of mineral substances which are not attacked masses of alumina, corunduni, magnesium oxide and the like are particularly suitable for making the furnace bottoms. The liquid aluminum cathode which separates the melt of cryolite from the mineral bottom, protects the bottom from attack by the melt.

A coating of compressed carbon as a protective layer over a less suitable stone bottom, such as chamotte for example, does not-in any way alter the invention, as this rammed "or compressed material is no longer being considered for the supplying of current and consequently is not heated by the passage of current. 1

As contrasted with the furnaces hithert known the new furnace permits of complete insulation of the furnace bottom.

The furnace is also suitable for the electrolytic production of other metals, such as 5 calcium, magnesium or the like.

' What I claim is:

1. For the production ofmetallic alumi-- num from molten aluminous materials by electrolysis, an electric furnacehaving a fur o nace bottom consisting of mineral substances that are not attacked by molten aluminum, thermal insulating meansfor said furnace bottom, a cathode of molten aluminum on the said bottom, an anode in said furnace 5 above said cathode, blocks of graphite in direct contact with the molten aluminum cathode, and means for supplying electric current to the anode and to said blocks of graphite.

o 2. For the production of metallic aluminum from molten aluminous materials by electrolysis, an electric furnace having a fur.

nace bottom consisting partly of mineral substances that are not attacked by molten aluminum, thermal insulating means for said \furnace bottom, a cathode of molten aluminum on the said bottom, an anode in said furnace above said cathode, blocks of graphite in direct contact with the molten aluminum cathode, and means for supplying electric current to the anode and to the said blocks of graphite.

' 3. For the production of metallic aluminum from molten aluminous materials by electrolysis, an electric furnace having a furnace bottom consisting of mineral substances that are not attacked by molten aluminum, thermal insulating means for said furnace bottom, a cathode of molten aluminum on 9 the said bottom, an anodein said furnace above said cathode, blocks of graphite, not

' forming part of the furnace bottom, 1n direct contact with the molten aluminum cathode, means for supplying electric current to the anode and to the said blocks of graphite,

and means for thermally insulating the furnace.

In testimony whereof I have afiixed my signature. EWIN RICHARD LAUBER. 

